David M. Kopec, Extension Turfgrass Specialist
The conversation often arises in Arizona regarding "hard and soft water," and how this affects irrigation. A common misconception is that "hard water" is bad for irrigating lawns and shrubs. Therefore, I need to have a "water softener" installed.
Well, there are really two and perhaps three things to think about here:
1. Perhaps, the homeowner may actually first be confusing water and/or soil salinity with hard water.
2. What is hard water?
3. What is soft water?
This issue deals with water salinity. Next month's issue will address "hard" and "soft" water, which are very different. Soil and water salinity will stress plants, both turf, and any irrigated trees and shrubs.
Water quality tests from an agricultural lab will test a water sample for salt levels. Salts in the water change the chemical properties of the water. Basically, salts (when dissolved in the water) compete with water itself, to behave as pure water. Turfgrass and landscape plants find it very easy to take up pure water. This is because pure water is not "distracted" by the salts.
If salt levels increase in irrigation water (either domestic or non-domestic water), it becomes harder for lawns and landscape plants to "take-up water," even though the soil is moist. Therefore, salty water actually requires more of the same salty water to keep the lawn and shrubs alive! Consequently, the more salty the water, the more often you need to irrigate.
Also in this case, you can apply more water than the grass needs. This causes leaching, with is very necessary. Leaching washes away the salts in the soil, with newer, "fresh" water, even if it is the same salty water you are using all along.
These practices cause the necessary leaching of salts - - away from the turfgrass roots. The result is the constant prevention of salt build-up in the SOIL, which itself is the determining factor on lawn and shrub performance.
In lawns that have poor drainage, salts can build up over time, even though salt levels in the water may be "low" or "medium." This is because the salts have nowhere to go! The salts move with the water, thanks to gravity. If any layering occurs in the soil, and different strata occur, drainage will be inhibited. That's why 2.0 inches of "soil" dumped on top of a "rock-hard" soil can eventually lead to a salt problem. That's why a hard-pan of caliche 3.0 inches below the turf soil impedes drainage, and a potential soil salt problem may be caused over time.
Homeowners often see white salt crusts on the soil at the edge of the lawn, or around the edge of plant berms. And yet, the plants or shrubs are not showing any stress, and look completely normal. The "surface salt" that you see here are salts that are evaporating along the edge of the soil, that was NOT ACTUALLY IRRIGATED. In these spots, the water has evaporated from the soil surface, which leaves the salts behind. You don't see salts close to the shrubs, or within the lawn itself, because the water has moved down in the soil, and this also minimizes evaporation at the surface.
Solutions to using saline water
In all practicality for homeowners, the water salt load is rarely critical – because you're using "drinking water." Almost all lawns and shrubs can tolerate our "drinking water" in Arizona. For people who manage large turf acreages (golf courses, parks, etc.), other water sources may be used. Water salinity may be much different (greater) from these sources than domestic water. If salt crystals appear within the middle of the lawn, you need to apply more [of the same water source] to wash the salts down.
To help increase the downward movement of water, it is best to poke holes in the lawn, using a power driven aerifier. These machines poke holes 2-3 inches in the ground. You should leave the holes open. The grass will actually fill in the holes. Don't be tempted to, or feel that you must "fill in" the holes with sand. Rake up the soil cores, or grind them up in place with a rotary mower. The open holes are more important to have to keep the salt levels tolerable.
Bermudagrass is quite salt tolerant. Tall fescue and ryegrass are moderately salt tolerant. Kentucky bluegrass is less salt tolerant than the above. Remember that salt stress causes the turf to look like it needs water! The grass will be dark blue-green in color, it will start to "wilt" and "curl" even though the soil is moist (screw driver goes in easily).
If your lawn suffers from salt stress, you can also help the lawn by mowing the turf at a higher mowing height that it is set for currently. This is not a problem for common bermudagrass, E-Z Turf, Midiron bermuda, or 99% of the improved seeded lawn type bermudagrass varieties, tall fescue, perennial ryegrass, and most lawn type Kentucky luegrass. Raising the height on Tifway (419) bermudagrass above 1-1/2 inches can often result in a scalped lawn, even if you mow three times/week. This is because most of the leaves will "migrate" to the end of the upright stems. When you mow off the tips of the stems, you can actually remove a lot of the leaves – because they are located at the tips of the stems. They exist at the tip, because of the unusually higher mowing height. Normally, when Tifway (419) Bermuda is mowed at ¾", three times per week with a sharp reel-type mower, the stems grow along the ground. The leaves are more evenly spaced across the entire length of the stem. So, less scalping occurs on Tifway when it gets mowed regularly at 3/4" or less.
Always remember, scalping a lawn is bad. Scalping a lawn that has salt stress is very bad.
To figure out how much salt is in your irrigation water, contact your local County Extension Office. They will give you an address for labs that will test samples.
Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, James A. Christenson, Director, Cooperative Extension, College of Agriculture & Life Sciences, The University of Arizona. The University of Arizona is an equal opportunity, affirmative action institution. The University does not discriminate on the basis of race, color, religion, sex, national origin, age, disability, veteran status, or sexual orientation in its programs and activities.